An imaging lens includes a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group having negative refractive power, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens having positive refractive power, and a third lens having negative refractive power. The second lens group includes a fourth lens and a fifth lens. The third lens group includes a sixth lens having negative refractive power and a seventh lens having negative refractive power. The first lens, the second lens, the third lens, and the seventh lens have specific Abbe's numbers. The first lens and the second lens have specific focal lengths.